I used Wakka, Rikku and Yuna. All overdrives were on comrade mode. Wakka would use Attack Reels, Yuna would use Auto-Life/Full-Life/Curaga or Entrust, and Rikku would use Mix to give everone Auto-Life (look up with items make that combo). So when Nemesis counters and kills everyone, the Auto-Life would revive them and they would have Overdrive charged. As long as you always have Auto-Life you should be ok. Wakka was the only one who did any damage in this fight.